Filter media construction using PTFE film and carbon web for HEPA efficiency and odor control

ABSTRACT

Disclosed herein, among other things, is an improved filter media construction that comprises multiple layers for improved odor control that can be used for vacuum cleaner air filtration cartridge applications. The filter media comprises anti-microbial ePTFE HEPA filter media to prevent mold growth. The filter media may also be used for air cleaner filtration, central air filtration for home and industrial buildings (HVAC), cleanrooms, and microelectronic devices. In an embodiment, the improved filter media construction comprises at least a PTFE layer, a bi-component layer, and a base layer. In an embodiment the PTFE layer comprises ePTFE. In an embodiment, the bi-component layer comprises non-woven polyethylene/polyethylene terephthalate (PE/PET). In yet another embodiment, the base layer comprises activated carbon. Other aspects and embodiments are provided herein.

This application is being filed as a PCT International Patentapplication on Jul. 22, 2010, in the name of Donaldson Company, Inc., aU.S. national corporation, applicant for the designation of allcountries except the U.S., and Kirit Patel, a U.S. Citizen, applicantfor the designation of the U.S. only, and claims priority to U.S.Provisional Patent Application Serial Number 61/227,784, filed Jul. 22,2009, the contents of which is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates generally to a layered filter media.

BACKGROUND OF THE INVENTION

Allergy sufferers and those with respiratory conditions are oftensensitive to particulate materials in the air. Vacuum cleaners and aircleaner filtration devices seek to remove particulate materials in homesand places of business, requiring filters to trap these particles.Without such filters, vacuum cleaners would simply re-circulate theparticulate matter back into the air. Industrial dust collectionequipment is required to remove greater proportions of smaller andsmaller particles from process air streams due to increasingly stringentregulatory requirements. Gas turbine intake filtration systems also mustremove quantities of very small particles as the presence of suchparticles can cause irreparable damage to turbine blades. Thecleanliness of an environment, the health of its occupants, theeffectiveness of industrial processes, the maintenance of industrialequipment, and the overall aesthetics of living require that submicronparticulate materials be readily removed by filter from an air stream.

In order to achieve submicron particulate removal from air streamspassing through such systems, inertial separators tend to simply place aphysical barrier in the path of particulate material that is thenknocked from the air stream into a collection bin. Paper bag dustcollectors are simply filters based on paper filter technologies in abag form. Such paper bags typically simply fit across the air stream forthe purpose of separating particulate from the air stream.

Newer filters have been designed with a collection filter or a flatpanel or cylindrical cartridges. In these applications, a HEPA filteringmaterial is used. By definition, HEPA filters remove at least 99.97% ofairborne particles 0.3 μm in diameter or larger. Because of theirgeneral reliability and high level of performance, HEPA filters areoften used to minimize the release of radioactive materials, asbestos,lead, beryllium, and other toxic particulates. In vacuum cleaners, HEPAfilters are used for air pollution control. Often HEPA structuresinclude an expanded PTFE (ePTFE), layer with a layer of a melt blownfiber combined in a filter construction, or a cellulose filter paperlayer with a layer of melt blown fiber combined in a filterconstruction. These structures are often cleaned by rapping the filteror by blowing filter cake or particulate from the filter usingcompressed air streams.

The filtration efficiency and cleanability of newer filters isimportant. These filters must be able to remove dust and dirt but mustbe easily cleanable without damage to the filter. Often cleaning dirtyfilters by rapping the filter on a solid object to dislodge dust anddirt can cause the filter media to fail or can cause multilayeredelements to delaminate, thus causing the filter to fail through theformation of a pathway for the dust and dirt through the filterstructure. Another failure mode occurs when fine dust particles aretrapped into the depth of the filter media, such that the dust cannot bedislodged by typical filter cleaning mechanisms, resulting in reducedvacuum power and shorter filter life.

One example of a dust filter vacuum technology using a fine fiber layerin a vacuum bag is Emig et al., U.S. Pat. No. 6,395,046. One example ofa filter cartridge in a wet/dry vacuum using expanded PTFE is Scanlon etal., U.S. Pat. No. 5,783,086. Filter materials, such as scrimmed HEPAmedia, often have high efficiency but often have short lifetimes and canbe degraded through water exposure.

There remains a need for a filter media construction suitable forremoving odor while maintaining a lower pressure drop and higherefficiency. Additionally, there exists a need for a filter mediaconstruction that provides HEPA efficiency, odor control, andanti-microbial treatment with a single medium to control mold growth incartridge media.

SUMMARY OF THE INVENTION

The present invention relates generally to multi-layered HEPA filtermedia for improved odor control and filtering. The present inventionprovides a multi-layered anti-microbial ePTFE HEPA filter media forimproved odor control. The media is specifically designed for vacuumcleaner air filtration cartridge application, but it can also be usedfor a variety of other filtration systems. Such systems include but arenot limited to air cleaner filtration, central air filtration for homeand industrial buildings (HVAC), clean rooms, and microelectronicdevices.

The filter media construction typically comprises at least three layers:an upstream media layer, a bi-component polyethylene/polyethyleneterephthalate (PE/PET) layer, and a base layer. In one embodiment, PTFEis used for the upstream media layer. In another embodiment, the PFTEused for the upstream media layer is expanded PTFE (ePTFE). The ePTFEfilm layer provides several important benefits to the filtration media,including HEPA efficiency and tap cleanability with minimal pressuredrop at HEPA efficiency. In an embodiment, the bi-component layercomprises non-woven polyethylene/polyethylene terephthalate (PE/PET). Incertain embodiments the base layer comprises activated carbon.

This summary is an overview of some of the teachings of the presentapplication and is not intended to be an exclusive or exhaustivetreatment of the present subject matter. Further details are found inthe detailed description and appended claims. Other aspects will beapparent to persons skilled in the art upon reading and understandingthe following detailed description and viewing the drawings that form apart thereof, each of which is not to be taken in a limiting sense. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in connection with thefollowing drawings, in which:

FIG. 1 is a schematic front perspective view of the filter constructionin accordance with the present invention.

FIG. 2 is a cross sectional view of a multi-layered filter media inaccordance with an embodiment of the invention.

FIG. 3 is a scanning electron microscope micrograph of the filter mediashown in FIG. 2.

FIG. 4 is a cross sectional view of a multi-layered filter media inaccordance with an embodiment of the invention.

FIG. 5 is a cross sectional view of a multi-layered filter media inaccordance with an embodiment of the invention.

FIG. 6 is a cross sectional view of a multi-layered filter media inaccordance with an embodiment of the invention.

FIG. 7 is a cross sectional view of a multi-layered filter media inaccordance with an embodiment of the invention.

FIG. 8A shows test results from conducting off-gassing tests where mediamade in accordance with the invention was challenged with ammonia

FIG. 8B shows test results from conducting off-gassing tests where mediamade in accordance with the invention was challenged with H₂S.

FIG. 9 shows the fractional efficiency for two different samples of themedia used in an embodiment of the invention.

While the invention is susceptible to various modifications andalternative forms, specifics thereof have been shown by way of exampleand drawings, and will be described in detail. It should be understood,however, that the invention is not limited to the particular embodimentsdescribed. On the contrary, the intention is to cover modifications,equivalents, and alternatives falling within the spirit and scope of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The market for general-purpose vacuum cleaners and for wet/dry vacuumsystems has imposed increasingly high standards of performance for thevacuum cleaners and their filters over recent years. The devices arerequired to remove greater and greater proportions of smaller andsmaller particles from streams obtained by the vacuum cleaner fromoften-harsh wet or dry environments in the home, garage, basement, shop,yard, and a variety of industrial environments. The increasedrequirements satisfy needs for improved health, reduced allergies,improved cleanability, reduced ambient particle counts, and otherrequirements for home, shop, and industrial environments.

The prior art filter media has had adequate performance in assignedroles in filtration equipment and processes. However, these media allsuffer from various problems. At present, filter technology providesodor control, but improved odor control is desired. Damp filters oftenfacilitate unwanted mold and mildew growth on the filters. The mold inturn produces mold spores, which can add pollution to the air.Additionally, it is typical that filters that can achieve a desiredefficiency for residential or other non-industrial applications oftenresult in a pressure drop across the filter media that is too high forthe applications.

The present invention provides a multi-layered anti-microbial ePTFE HEPAfilter media for improved odor control. The media is specificallydesigned for vacuum cleaner air filtration cartridge application, but itcan also be used for a variety of other filtration systems. Such systemsinclude but are not limited to air cleaner filtration, central airfiltration for home and industrial buildings (HVAC), cleanrooms, andmicroelectronic devices.

Filter Construction

Referring to FIG. 1, the filter media construction 10 of an exampleembodiment comprises at least three layers: an upstream media layer 20,a bi-component (PE/PET) layer 30, and a base layer 40. In use, air flowstarts from the upstream media layer 20, passes through the bi-componentlayer 30, and exits through the base layer 40.

In one embodiment, PTFE is used for the upstream media layer 20. In atypical embodiment, the PFTE used for the upstream media layer 20 isexpanded PTFE (ePTFE). The ePTFE film layer provides several importantbenefits to the filtration media, including optional HEPA efficiency andtap cleanability with minimal pressure drop at HEPA efficiency. HEPAefficiency is defined as a minimum 99.97% at 0.3 micron particles (U.S.standard).

In one embodiment, the base layer 40 comprises an activated carbonlayer, and the upstream media layer 20 is ePTFE. In another embodiment,the activated carbon layer comprises a minimum of 45% activated carbon.The ePTFE filtration layer is bonded using a low melt bi-component layer30 with carbon based media under heat and pressure.

FIG. 2 shows one embodiment of the present invention where the upstreammedia layer 20 comprises ePTFE film, the bi-component layer 30 isnon-woven PE/PET, and the base layer 40 comprises activated carbon. Thebi-component layer 30 may be treated with an anti-microbial substance.As shown in FIG. 2, the bi-component layer 30 may also be alternativelyformed using a low melt adhesive web. Additionally, the base layeractivated carbon may be treated with an anti-microbial substance. FIG. 3shows a scanning electron microscope micrograph of the filter mediashown in FIG. 2.

In one embodiment, the base layer 40 comprises activated carbon andnanofiber, and the upstream media layer 20 is PTFE, as shown in FIG. 4.

In one embodiment, the base layer 40 is melt-blown media with carbonparticles, and the upstream media layer 20 is PTFE, as shown in FIG. 5.

In one embodiment, the base layer 40 is particle laden melt-blownnanofiber with carbon particles, and the upstream media layer 20 isPTFE, as shown in FIG. 6.

In one embodiment, the base layer 40 is particle laden melt-blownmaterial further containing carbon particles, and the upstream medialayer 20 is nanofiber created by Donaldson Company, Inc. of Bloomington,Minn. This embodiment is shown in FIG. 7. In one embodiment, thenanofiber may be coated on one side. In another embodiment, thenanofiber may be coated on two sides. In the various embodimentsnanofiber media may be co-pleated with other media, such as carbonloaded melt blown media.

Exemplary Materials

The present invention may be constructed with a variety of materials.HEPA filtering material is preferred as, by definition, HEPA filtersremove at least 99.97% of airborne particles 0.3 μm in diameter.However, due to the construction of the filter, the starting materialsused to construct the filters of the present invention need not be HEPAefficiency in order for the entire filter media construction to be HEPAefficiency. In one embodiment, polytetrafluoroethylene (PTFE) is usedfor the upstream media layer. Expanded PTFE (ePTFE) may also be utilizedin the present invention. Typically, ePTFE media have very high pressuredrops and moderate HEPA efficiency.

Alternatively, as shown in FIG. 7, the upstream media layer 20 maycomprise nanofiber, such as that created by Donaldson Company, Inc. ofBloomington, Minn. These nanofibers provide a low cost option withmid-range filtration efficiency. Examples of these nanofibers includesome coated on one side and others coated on two sides, co-pleated orbonded with melt-blown carbon media. The melt-blown carbon media isavailable from a variety of commercial sources, such as Hollingsworthand Vose of East Walpole, Mass.

In one embodiment, the bi-component layer 30 may comprisepolyethylene/polyethylene terephthalate (PE/PET). In another embodiment,the bi-component layer 30 may comprise a low melt adhesive web.

In one embodiment, the base layer 40 comprises activated carbon. In apreferred embodiment, the base layer 40 comprises a minimum of 45%activated carbon. The base layer may be produced with or withoutanti-microbial treatment. Alternatively, the base layer 40 comprisesnanofiber with activated carbon. In this application, the nanofibersserve a multifunctional purpose: in addition to helping to captureairborne contaminants that escape ePTFE film, the nanofibers cause theoverall pressure drop to be lower than if PTFE film alone is used.Consequently, use of these materials does not necessitate that thestarting PTFE film be HEPA efficiency.

In another embodiment, the base media 40 comprises melt-blown media withcarbon particles. The melt-blown media with carbon particles serves dualpurposes: not only does it aid control odor, it also helps to captureairborne contaminants that escape the ePTFE film layer. Furthermore, theoverall pressure drop is lower than if PTFE film alone is used, so thestarting PTFE film need not be HEPA efficiency.

In yet another embodiment, the base media 40 comprises carbon particleladen melt-blown media with nanofibers. Such a material is suitable forremoving odor with lower pressure drop and higher efficiency. Thestarting PTFE film of this embodiment need not be HEPA efficiency.

One exemplary material that may be used for the base media 40 is a2-in-1 carbon substrate developed by Lydall, Inc. of Manchester, Conn.An example of such a material is C-680 ActiPure® media developed byLydall, Inc. of Manchester, Conn. The ActiPure® media comprises anon-woven material and activated carbon.

Interbasic Resources Inc. (IBR) performed efficiency and off-gassingtests on media, which is shown in FIGS. 8A and 8B. These tests weredeveloped by IBR for vacuum odor control. For the off-gassing tests, themedia was challenged with ammonia and H₂S.

FIG. 8A shows the test results from conducting off-gassing tests wherethe media was challenged with ammonia in order to determine offgassingfrom a loaded vacuum cleaner filter under static conditions. Thecontaminant used in the off-gassing test was 50 grams of IEC 60312household test dust saturated with ammonia at 200 ppm(v). The tests wereconducted at 70 degrees Fahrenheit with a relative humidity of 48% andbarometric pressure of 736 mmHg. The media samples tested were 12″×12″flat sheet media formed into a pocket and filled with 50 grams of dust.

FIG. 8B shows the test results from conducting off-gassing tests wherethe media was challenged with ammonia in order to determine offgassingfrom a loaded vacuum cleaner filter under static conditions. In thesetests, the contaminant used in the off-gassing test was 50 grams of IEC60312 household test dust saturated with H₂S at 200 ppm(v). The testswere conducted at 71 degrees Fahrenheit with a relative humidity of 47%and barometric pressure of 739 mmHg. The media samples tested were12″×12″ flat sheet media formed into a pocket and filled with 50 gramsof dust.

Another exemplary material for use in the base media 40 shown in FIG. 9shows the fractional efficiency of the material for two differentsamples of the media.

Additionally, the filter media 10 may be treated in any number of waysto improve its efficiency in removing minute particulates and for otherpurposes. For example, electrostatically treated media can be used, ascan cellulose media having one or more layers of fine fiber, or othertypes of media known to those skilled in the art. The filter media 10may also be treated with anti-microbial substances to prevent the growthof mold on the filters. Anti-viral or anti-mycotic agents may also beused to treat the filter media 10 to reduce the populations ofinfectious agents.

It should be noted that, as used in this specification and the appendedclaims, the singular forms “a,” “an,” and “the” include plural referentsunless the content clearly dictates otherwise. It should also be notedthat the term “or” is generally employed in its sense including “and/or”unless the content clearly dictates otherwise.

It should also be noted that, as used in this specification and theappended claims, the phrase “configured” describes a system, apparatus,or other structure that is constructed or configured to perform aparticular task or adopt a particular configuration. The phrase“configured” can be used interchangeably with other similar phrases suchas “arranged”, “arranged and configured”, “constructed and arranged”,“constructed”, “manufactured and arranged”, and the like.

All publications and patent applications in this specification areindicative of the level of ordinary skill in the art to which thisinvention pertains. All publications and patent applications are hereinincorporated by reference to the same extent as if each individualpublication or patent application was specifically and individuallyindicated by reference.

This application is intended to cover adaptations or variations of thepresent subject matter. It is to be understood that the abovedescription is intended to be illustrative, and not restrictive. Thescope of the present subject matter should be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

What is claimed is:
 1. A multi-layer filter media constructioncomprising: a non-HEPA upstream media layer, a bi-component layer, and abi-component layer, and a base media layer comprising activated carbon,wherein the upstream media layer is bonded to the base media layer bythe bi-component layer, and wherein the multi-layer filter mediaconstruction is HEPA.
 2. The filter media construction of claim 1, theupstream media layer comprising PTFE.
 3. The filter media constructionof claim 2, wherein the PTFE is expanded PTFE.
 4. The filter mediaconstruction of claim 1, the bi-component layer comprising non-wovenpolyethylene/polyethylene terephthalate.
 5. The filter mediaconstruction of claim 1 wherein the base layer comprises a minimum of45% activated carbon.
 6. The filter media construction of claim 1, thebase layer further comprising nanofiber.
 7. The filter mediaconstruction of claim 1, the base layer comprising carbon loadedmelt-blown media.
 8. The filter media construction of claim 1, the baselayer further comprising nanofiber.
 9. A method for making a HEPAthree-layer filter media construction comprising: bonding a non-HEPAupstream media layer to a base layer using a bi-component layer underheat and pressure, wherein the base layer comprises activated carbon.10. The method of claim 9, the upstream media layer comprising expandedPTFE.
 11. The method construction of claim 9, the bi-component layercomprising non-woven polyethylene/polyethylene terephthalate.
 12. Themethod of claim 9, wherein the base layer comprises a minimum of 45%activated carbon.
 13. The method of claim 9, wherein the base layerfurther comprises nanofiber.
 14. The method of claim 9, the base layercomprising carbon loaded melt-blown media.
 15. The method of claim 14,the base layer further comprising nanofiber.
 16. A multi-layer filtermedia construction comprising: an upstream media layer, that does notmeet HEPA standards, a bi-component layer, and a base layer comprisingcarbon loaded nanofiber, wherein the upstream media layer is bonded tothe base media layer by the bi-component layer, and wherein themulti-layer filter media construction meets HEPA standards.
 17. Thefilter media construction of claim 16 wherein the upstream layercomprises PTFE.
 18. The filter media construction of claim 16 whereinthe base layer comprises a minimum of 45% activated carbon.
 19. Thefilter media construction of claim 16 wherein the bi-component layercomprises non-woven polyethylene/polyethylene terephthalate.
 20. Thefilter media construction of claim 16, wherein the filter mediaconstruction further comprises an anti-microbial treatment.